1. Field of the Invention
The present invention relates to a transmission rate control method for controlling a transmission rate of uplink user data, based on a dedicated absolute transmission rate of uplink user data received at a mobile station via a dedicated absolute transmission rate control channel which is transmitted using a dedicated identifier for the mobile station or a common absolute transmission rate of uplink user data received at a mobile station via a common absolute transmission rate control channel which is transmitted using a common identifier for mobile stations which satisfy a predetermined condition, and a mobile station and a radio network controller which are used in the transmission rate control method.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Referring to FIG. 3, the mobile communication system, to which the “Enhanced Uplink” is applied, is explained. In FIG. 3, a serving cell for the mobile station UE is changed from cell#3 which is controlled by a radio base station Node B #1 to cell #4 which is controlled by a radio base station Node B #2. The serving cell mainly controls the transmission rate of uplink user data transmitted by the mobile station UE.
In addition, the mobile station UE is configured to switch a “dedicated transmission rate control (dedicated rate control)” and a “common transmission rate control (common rate control)” flexibly.
The “dedicated transmission rate control” means controlling the transmission rate of the uplink user data based on the dedicated absolute transmission rate of the uplink user data received at the mobile station UE via a “Dedicated Enhanced Absolute Grant Channel (E-AGCH, dedicated absolute transmission control channel)”, which is transmitted using the dedicated identifier for the mobile station UE.
The “common transmission rate control” means controlling the transmission rate of the uplink user data based on the common absolute transmission rate of the uplink user data received at the mobile station UE via a “Common Enhanced Absolute Grant Channel (E-AGCH, common absolute transmission control channel)”, which is transmitted using the common identifier for the mobile stations belonging to the specific cell (specific group).
Here, when the mobile station UE performing the dedicated transmission rate control receives the Common E-AGCH, the mobile station UE stores the common absolute transmission rate transmitted by the Common E-AGCH. When the Dedicated E-AGCH becomes “Inactive”, the mobile station UE updates the transmission rate of the uplink user data based on the stored common absolute transmission rate. Then, the mobile station UE controls the transmission rate of the uplink user data based on the common absolute transmission rate received via the Common E-AGCH.
Thus, the mobile station UE performing the dedicated transmission rate control can switch from the dedicated transmission rate control to the common transmission rate control smoothly, by storing the common absolute transmission rate transmitted by the Common E-AGCH.
However, in the conventional mobile communication system as described above, when the serving cell for the mobile station UE is changed due to the cell change, and when the common absolute transmission rate indicated by the Common E-AGCH which the current serving cell signals is drastically different from the common absolute transmission rate indicated by the Common E-AGCH which the previous serving cell signals, the mobile station UE is configured to transmit the uplink user data using the inappropriate transmission rate of the uplink user data toward the current serving cell, until the mobile station UE receives the Common E-AGCH from the current serving cell after the cell change.
Accordingly, there has been a problem that the radio resource is not used efficiently.